Abstract: A compound-channel Froude number is derived to reflect correctly the occurrence of minimum specific energy in open channels with overbank flow. The limitations of conventional Froude-number formulations are described and comparisons with the proposed compound-channel Froude number are presented. The results of a laboratory investigation into the occurrence of two points of minimum specific energy are presented, and this phenomenon can occur for certain compound-channel geometries as predicted by the compound-channel Froude number. The experimental investigation indicates that the upper point of minimum specific energy can properly be considered the limit of subcritical flow.